The Big Bang theory was started by a priest and, because of that, some scientists at the time (read about Fred Hoyle) really thought that it was only an attempt to give God a role to play in the creation of the universe. I'm sure that Father Lemaitre thought that there was divine intervention involved. However, he was also a university professor (mathematics and cosmology) so he made sure to tell his students that the theory was only the application of scientific knowledge; therefore, it should work, whether one believes in God or not.
Many religions assert (some of them somewhat violently) that they are the only true religion. Since dissimilar religions cannot be ALL the only true religion, then some religions MUST be wrong.
---
The Big Bang theory describes the behavior of a universe where the energy content is constant and where the energy density (a.k.a. the temperature of the universe) decreases as space expands. That is it. It is based on hypotheses that are supported by observation, and is supplemented by scientific principles from many different branches of science.
- The universe contains energy.
- Space expands.
- The universe appears hotter in the past.
When we use the theory backwards (to see what the universe could have looked like in the past) we hit a wall: at some point in the past, the energy density would have been so high that we no longer understand how things work. This moment is called the Planck Time.
There are a few things that we do understand about that moment:
- energy already existed (the Planck Time is NOT the creation of energy)
- space was already expanding (the Planck Time is NOT the creation of space)
- matter could not exist - it came into existence minutes after.
- the forces could not exist - they only came into existence seconds after
- even the fundamental particles could not exist
We are not sure if gravity existed at that moment but if it did not, it came into existence very soon after.